Self &amp; minus; adaptive weighted space time transmitting diversity method and system thereof

ABSTRACT

The present invention discloses a method of adaptive weighting space-time transmit diversity, comprising: symbols to be transmitted at a transmitting end being output after being space-time encoded according to certain regulation, and the current transmission powers of the two antennae being real-timely adjusted according to the given transmission power weight values; after the transmission powers are determined, the space-time encoded output signals being sent out at two independent antennas by transmitting antenna array in terms of the current transmission power; the fading characters of two wireless channels being estimated by the receiver at a receiving end according to the present received signals and then fed back to the transmitting end; the transmitting end receiving and obtaining the fading amplitude characters of two wireless channels through feedback channel, calculating new adaptive weight values of transmission powers, and adjusting transmission powers according to these weight values. The present invention also discloses a system for implementing the above method of adaptive weighting Space-time Transmit Diversity. In term of the method and structure, the transmission powers can be dynamically adjusted in adaptive weighting manner, in order to boost system performance gain.

FIELD OF THE TECHNOLOGY

The present invention relates generally to space-time transmit diversitytechnology, especially to a method of space-time transmit diversity forreal-timely adjusting signal transmission power in an adaptive mannerand a system therefore.

BACKGROUND OF THE INVENTION

In the standard of Third Generation (3G) Wideband CDMA (WCDMA) based onCode Division Multiple Access (CDMA), as all subscribers in the samecell and all subscribers in the adjacent cells share the identicalfrequency band at the same time, there is interference among thesubscribers, which restricts system capacity and data transmission rate.To increase the system capacity, manifold diversity methods can beadopted, such as the technology of multi-path diversity, space diversityand antenna diversity, etc. In the diversity-applied system technology,for one piece of information there are more than one independent copiesof different formats. After being received by a receiver, theseindependent copies are specially processed according to MaximumLikelihood (ML) Principle and by taking good use of informationredundancy. By doing this, the bit rate error of informationtransmission is greatly reduced and transmission power of wireless datais decreased, consequently the interference among subscribers beingreduced. It shows that system capacity can be effectively improved byusing diversity technology.

In the downlink channel of WCDMA system, to implement high-capacity ofsubscriber number and data transmission with high speed, manifoldtransmit diversity technologies are also to be applied, and space-timetransmit diversity (STTD) is one of those technologies, the content ofwhich being: the information to be transmitted being simply space-timeencoded, the space-time encoded signal being divided into two routeswhich are respectively sent to two independent transmitting channels fortransmission according to equal power principle; accordingly, thereceiving end respectively receiving the signals from two independenttransmitting channels and processing the received signals according toMaximum Likelihood (ML) Principle, as is shown in FIG. 1. In FIG. 1,sign 100 denotes the information to be transmitted, in which S₁ and S₂are two transmitting symbols in the same space-time encoding block; sign101 is the space-time encoding module; sign 106 is the transmittingantenna array, indicating that two dependent transmitting channelsperform transmission through antenna Ant1 and Ant2 respectively; Rec isthe receiver at the receiving end based on Maximum Likelihood (ML)Principle.

At the receiving end, the received signals of the same space-timeencoding module is expressed as follows: $\begin{matrix}\left\{ \begin{matrix}{r_{1} = {{h_{1}S_{1}} - {h_{2}S_{2}^{*}} + n_{1}}} \\{r_{2} = {{h_{1}S_{2}} + {h_{2}S_{1}^{*}} + n_{2}}}\end{matrix} \right. & (1)\end{matrix}$

In the equation, r₁, r₂ respectively being the received signals of thesame space-time encoding module, h₁ and h₂ respectively being the fadingfactors of wireless channel between sending antenna and receivingantenna; n₁ and n₂ being the receiving noises. According to MaximumLikelihood (ML) receiving principle, Signal Noise Ratio (SNR) of judgingvariable can be computed as: $\begin{matrix}{{SNR}_{STTD} = {\frac{2\sigma_{0}^{2}}{\sigma^{s}}E_{s}}} & (2)\end{matrix}$

In the equation, E_(s) being signal transmission power, σ² being systemnoise power, σ₀ ² being wireless channel fading character.

In the above method, transmission power is equally divided into twoantennas all and singular and the transmission power is not properlydistributed between different antennas in terms of certain principle, asa result the best performance is not reached and optimal transmissioneffect is unattainable.

SUMMARY OF THE INVENTION

Since the fading of two transmitting channels are independent of eachother, if there is feedback channel, system performance can be furtherimproved by feeding back the present wireless channel informationreceived at the receiving end to the transmitting end so that thetransmitting end can properly distribute transmission power according tothe feedback information.

Based on the above ideas, a main object of the present invention is toprovide a method of adaptive weighting Space-time transmit diversity fordynamically adjusting transmission power in adaptive weighting manner,in order to improve system performance gain. This method is also easilyhandled and flexible.

Another object of the present invention is to provide a system forimplementing the method of adaptive weighting space-time transmitdiversity, which can accomplish real-timely and dynamically adjustingtransmission power. The design of this system is simple and theimplementation is easy, consequently the system performance ofspace-time transmit diversity is further improved.

To achieve the above-mentioned object, the specific technical scheme ofthis invention is as follows.

A method for adaptive weight space-time transmit diversity, comprises:

-   -   a. for the symbols to be transmitted at a transmitting end,        every two input symbols being made a block and two routes of        signals being output after being space-time encoded according to        certain regulation;    -   b. at the transmitting end, the current transmission powers of        two transmitting antenna channels being real-timely adjusted        respectively according to the currently prescribed power weight        values, under the precondition of holding the gross transmission        power invariable;    -   c. after the transmission powers are determined, the space-time        encoded output signals being sent out at two independent        antennas by the transmitting antenna array in terms of the        current transmission powers;    -   d. the fading characters of two wireless channels being        estimated by the receiver at a receiving end according to the        present received signals, the fading amplitude characters of the        two wireless channels being encoded and then being fed back to        the transmitting end;    -   e. the transmitting end receiving and obtaining the fading        amplitude character information of two wireless channels through        a feedback channel, calculating the new adaptive transmission        power weight value of the two transmitting channels, and        adjusting transmission powers according to these weight values;

The above method may further comprise: for the initial transmission, thetransmitting end setting the transmission power weight values of the twoantennas as 1/sqrt (2.0) in terms of equal transmission power principle.

In the above scheme, step a further comprises: setting one of the twosignals to be the same as the input block signal, and another signal tobe the conjugate inverted sequence of input block signal and the firstoutput symbol being inversed.

Step b further comprises: the adjustments of the transmitting end powerbeing in the coherent time of wireless channel and performedreal-timely, with a time slot as a unit.

In step e, the step of the transmitting end receiving the fadingamplitude character information of wireless channels, further comprises:

-   -   e1. a feedback signal processing module collecting the        separately distributed Feedback Information (FBI) bits;    -   e2. the feedback signal processing module incorporating the        collected FBI bits;    -   e3. the feedback signal processing module decoding the        incorporated FBI, obtaining the values representing the fading        amplitude character of wireless channels, which are imported to        an optical weight calculating module.

In step e, setting Feedback Information (FBI) field of uplinktransmission as the feedback channel, and the estimated fading amplitudecharacter information of the two wireless channels being sent to thetransmitting end through the feedback channel.

In step e, the adaptive weight values can be calculated according to thefading amplitude characters of the two wireless channels, or accordingto the ratio of the two wireless-channel fading amplitudes.

In the present invention, a system for implementing the said method ofadaptive weighting space-time transmit diversity is also provided, atleast comprising a space-time encoding module at the transmitting end, atransmitting antenna array with two antennae and a receiver with maximumlikelihood receiving module at the receiving end. The key is that thetransmitting end further comprising a transmission power distributingmodule, a feedback channel, a feedback signal processing module and anoptical weight calculating module.

After being encoded by the space-time encoding module, the symbols to betransmitted are sent out as two routes of signals; the transmissionpower distributing module adjusts the transmission powers of the twotransmitting antenna and then sends out the two routes of signals fromthe two antennas in the transmitting antenna array; the receiver at thereceiving end receives and processes the transmitted signals and thenfeeds back the fading amplitude character information of the currentwireless channels to the feedback signal processing module at thetransmitting end through feedback channel, the values gained after theprocess are sent to the optical weight calculating module forcalculating new transmission power weight values, and the new weightvalues are sent to the transmission power distributing module foradjusting transmission powers.

In the above system, the said feedback channel is carried by theseparately distributed FBI bits in a physical channel.

From the above scheme, the key of the present invention lies in that thetransmitting end recalculating proper transmission power weight valuesaccording to the received fading amplitude character information of thecurrent two wireless channels, redistributing transmission power inorder to improve system performance.

The method of adaptive weighting space-time transmit diversity and thecorresponding system provided in the present invention take on theflowing advantages and characteristics:

1) In the present invention, the optical transmission power weightvalues of different antenna can be calculated according to the feedbackthe fading amplitude information concerning the wireless channels, inorder to properly distribute transmission power and greatly improvesystem performance without adding antenna and other devices. Comparingwith the prior STTD, the performance can be improved to 1.55 db.

2) In the present invention, the optical weight values can be calculatedonly according to the ratio of amplitude characters of the two wirelesschannels by feeding back to the transmitting end, in which requirementfor feedback channel capacity is greatly decreased.

3) In the present invention, transmission power values are adjustedreal-timely according to the currently received wireless channelcharacter information to form adaptive adjusting mechanism with simpleand flexible operation.

4) In the present invention, only the transmission power distribution,the feedback signal processing and the optical weight calculatingmodules are added, making little change to the existing system, withsimple design and easy implementation.

5) It's testified through simulation tests and theoretical analysis, interms of the method and system of the present invention, the error rateis much lower than that of the prior STTD in condition of equal signalnoise ratio (SNR); what's more, in condition of equal error rate, thetransmission power required by the present invention is much lower.Therefore, the more signal noise ratio (SNR) increases, the moreperformance gain of the system increases.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the sketch demonstrating the system composition structure ofSTTD in the prior art;

FIG. 2 is the sketch demonstrating the system composition structure ofspace-time transmit diversity in terms of the present invention;

FIG. 3 is the flow chart demonstrating the space-time transmit diversitymethod in terms of the present invention;

FIG. 4 is the sketch demonstrating the performance contrast betweenspace-time transmit diversity in terms of the present invention and theprior art.

EMBODIMENTS OF THE INVENTION

Now, the present invention will be described in detail with reference tothe accompanying drawings and specific embodiments.

FIG. 2 is the sketch demonstrating the system composition structure ofspace-time transmit diversity in terms of the present invention. As isillustrated in FIG. 2, this system comprises space-time encoding module101, transmitting antenna array with two antennae 106 and a receiverconsisting of maximum likelihood receiving module; especially thetransmitting end comprises feedback channel 104, feedback signalprocessing module 102, optical weight calculating module 103 andtransmission power distributing module 105. Feedback channel 104 is usedto output information from the receiver concerning characteristics ofthe current wireless channel; feedback signal processing module 102 isused to receive information from the feedback channel concerningcharacteristics of the current wireless channel and perform mappingprocess; optical weight calculating module 103 is used to calculate thetransmission power weight values of the two transmitting channelsaccording to information from feedback signal processing module 102concerning characteristics of the current wireless channels;transmission power distributing module 105 is used to adjusttransmission power values of different antennae according to thereceived transmission power weight values; transmitting antenna array106 is used to send out the output encoded by space-time encoding module101 through two independent antennae, according to the currenttransmission power values.

Based on the above system of space-time transmit diversity, theimplementing method of the present invention is demonstrated in FIG. 3,at least comprising:

1) The transmitting end performing space-time encoding for the symbolsto be transmitted in term of certain regulation, and the input symbolsbeing output in two routes with two symbols (S₁, S₂) as a block: oneroute staying the same with input block, namely outputting (S₁, S₂),another being the conjugate inverted sequence of input block signal andthe first output character being inversed, namely (−S₂*, S₁*).

2) Under the precondition of holding the total transmission powerinvariable, the transmitting end respectively adjusting the currenttransmission power values of the two antennae according to the currentgiven transmission power weight values in real-time, properlydistributing transmission powers of the two transmitting channels.

As to the initial transmission, the initial transmission power weightvalue of every antenna is set according to equal power principle, namelyw₁=w₂=1/sqrt (2.0)=0.707.

The adjustment of transmission power is a multiplicative operation inreal number in fact, the symbols after multiplicative operation beingmodulated to analog signal, then being radiated by a radio-wavefrequency module. This adjustment of power is often real-timely carriedout in the coherent time of wireless channel with the time slot as theunit.

3) After the transmission powers are determined, the transmittingantenna array sending out the space-time encoded output signals throughthe two independent antennae, according to the current transmissionpower values.

4) The receiver at the receiving end incorporating the received tworoutes of signals according to Maximum Likelihood (ML) receivingprinciple, estimating wireless channel responses respectively andfeeding back the responses to the transmitting end, the responses beingmapped by the feedback signal processing module and then sent to theoptical weight calculating module.

In the existing standard system, because the logical feedback channelsare carried by the separately distributed Feedback Information (FBI)bits in the physical channel, a special module is needed at transmittingend to collect and incorporate the separate FBI bits, obtaining a valuewhich can directly represent the ratio of wireless channel fadingamplitudes needed for weight value calculation, or encoding the ratio asbit flow to transfer with reference to a certain encoding mode.Therefore, the said mapping process means: obtaining the needed realvalue through the course of “FBI bits reception”→“FBI bitsincorporation”→“FBI decoding”, and this value being used as an inputparameter for the calculation of transmission power weight values.

5) Then, according to the fading amplitude character information ofwireless channels and in term of equation (3), the optical weightcalculating module calculating the new adaptive transmission powerweight values w₁, w₂ of the two transmitting channels, and adjustingtransmission powers of the two antennae. $\begin{matrix}\left\{ \begin{matrix}{w_{1} = \frac{{h_{1}}^{2}}{\sqrt{{h_{1}}^{4} + {h_{2}}^{4}}}} \\{w_{2} = \frac{{h_{2}}^{2}}{\sqrt{{h_{1}}^{4} + {h_{2}}^{4}}}}\end{matrix} \right. & (3)\end{matrix}$

-   -   where h₁ and h₂ being the feedback fading amplitude character        information of wireless channels.

Since equation (3) can be simplified in another implementing form, theadaptive weight values can be directly calculated according to the ratiobetween the fading amplitudes of the current two wireless channels,namely: $\begin{matrix}\left\{ \begin{matrix}{w_{1} = {\frac{1}{\sqrt{1 + \left( {{h_{2}}/{h_{1}}} \right)^{4}}} = \frac{1}{\sqrt{1 + R^{4}}}}} \\{w_{2} = {\frac{1}{\sqrt{1 + \left( {{h_{1}}/{h_{2}}} \right)^{4}}} = \frac{1}{\sqrt{1 + \left( {1/R} \right)^{4}}}}}\end{matrix} \right. & (4)\end{matrix}$

-   -   where R≢|h₂|/|h₁| being the ratio between the fading amplitudes        of the two wireless channels.

In practical application, other methods can be adopted when calculatingtransmission power weight values. However, it's testified by a series oftheoretical calculation and abstract tests that equation (3) andequation (4) are the optimum. The optimum is externalized in twoaspects: one is the performance gain obtained in the equations, reaching1.55 dB comparing with the equal-weight manner in the prior art; anotheris the convenience for implementation, because generally as to otherunequal-weight manners both amplitude information and phase informationof the two wireless channel responses need being fed back, while as tothe present scheme only the amplitude ratio information of the twowireless channel responses, in this way requirement for feedback channelcapacity is greatly decreased, and the reliability of feedbackinformation is greatly improved in condition of settled feedback channelcapacity.

FIG. 4 is the sketch demonstrating the performance contrast betweenspace-time transmit diversity in terms of the present invention and theprior space-time transmit diversity. Therein, the abscissa indicates thedB value of signal noise ratio (Eb/No), and the ordinate indicates rawerror rate, curve 41 is the performance curve of the prior STTD, curve42 is the performance curve of the STTD after adaptive weightingadjustment of transmission power is added in terms of the presentinvention. It can be seen that when error rate is the same, the signalnoise ratio after adding adaptive weighting adjustment of transmissionpowers is lower than that of the prior STTD, in another way, incondition of equal error rates, lower transmission power is required interms of the present invention; from another point of view, when thesignal noise ratios of the two curves are the same, the error rate afteradding adaptive weighting adjustment of transmission powers isapparently lower than that of the prior technology. Obviously, theperformance of transmitting diversity in term of the present inventionis improved.

The above description is just a better embodiment of the presentinvention, not necessarily confining the protection range of thisinvention.

1. A method of adaptive weighting space-time transmit diversity,comprising: a. at a transmitting end, according to a certain regulation,space-time encoding symbols to be transmitted, every two input of whichare made as a block, and then outputting two routes of signals; b.real-timely adjusting current transmission powers of two transmittingantennas respectively according to currently prescribed transmissionpower weight values, under the precondition of holding the grosstransmission power of two transmitting antennas invariable; c. after thetransmission powers are determined, transmitting the space-time encodedoutput signals at the two independent antennas by a transmitting antennaarray in terms of the current transmission powers; d. at a receivingend, estimating fading characters of two wireless channels by a receiveraccording to the present received signals, encoding fading amplitudecharacters of two wireless channels and then feeding back to thetransmitting end; e. at the transmitting end, receiving and obtainingthe said fading amplitude character information of two wireless channelsthrough a feedback channel, calculating new adaptive transmission powerweight values in the two transmitting channels, and adjusting thetransmission powers according to the said weight value.
 2. The methodaccording to claim 1, further comprising: for the initial transmission,at the transmitting end setting the said transmission power weight valueof the two antennas as 1/sqrt (2.0) in terms of equal transmission powerprinciple.
 3. The method according to claim 1, step a furthercomprising: setting one route of the two signals to be the same as theinput block, and another to be the conjugate inverted sequence of theinput block, and the first output symbol being inversed.
 4. The methodaccording to claim 1, step b further comprising: at the transmittingend, real-timely adjusting the transmission power in the coherent timeof wireless channel, with a time slot as a unit.
 5. The method accordingto claim 1, at the transmitting end receiving the fading amplitudecharacter information of wireless channels of step e, furthercomprising: e1. collecting distributed separately Feedback Information(FBI) bits by a feedback signal processing module; e2. incorporating thecollected FBI bits by the feedback signal processing module; e3.decoding the incorporated FBI by the feedback signal processing module,obtaining the values representing the fading amplitude characters ofwireless channels, and then inputting to an optical weight calculatingmodule.
 6. The method according to claim 1, step e further comprising:calculating the adaptive transmission power weight values according tothe fading amplitude characters of the two wireless channels.
 7. Themethod according to claim 1, step e further comprising: calculating theadaptive transmission power weight values according to a ratio of thetwo wireless-channel fading amplitudes.
 8. The method according to claim1, step e further comprising: setting Feedback Information (FBI) fieldof uplink transmission as the feedback channel, and sending theestimated fading amplitude character information of the two wirelesschannels to the transmitting end.
 9. A system for implementing anadaptive weighting space-time transmit diversity, at least comprising: aspace-time encoding module at a transmitting end, a transmitting antennaarray with two antennae and a receiver with maximum likelihood receivingmodule at a receiving end, wherein the transmitting end furthercomprises a transmission power distributing module, a feedback channel,a feedback signal processing module and an optical weight calculatingmodule; wherein after being encoded by the space-time encoding module,symbols to be transmitted are sent out as two routes of signals; thetransmission power distributing module adjusts the transmission powersof the two transmitting antenna and then sends out the two routes ofsignals from the two antenna in the transmit antenna array, the receiverat the receiving end receives and processes the transmitted signals andthen feeds back fading amplitude character information of the currentwireless channels to the feedback signal processing module at thetransmitting end through the feedback channel, values gained after theprocess are sent to the optical weight calculating module forcalculating new transmission power weight values, and the new weightvalues are sent to the transmission power distributing module foradjusting the transmission powers.
 10. The system according to claim 9,further comprising: the said feedback channel is carried by separatelydistributed FBI bits in a physical channel.